The invention relates to implantable cardiovascular devices and more in particular to cardiac-valve prosthetic devices that fall within the IPC (International Patent Classification) A61F2/24. There exist various prosthetic devices for correcting defects of heart valves, from simple annuloplasty rings, to be integrated in the natural heart valves of the patient for re-establishing proper functionality thereof, to valve prostheses proper that altogether replace the natural heart valves and that may be of a mechanical type (MHV), of a tissue type (THV), or a transcatheter tissue type (TAVI).
After implantation, the state of operation of heart valve prostheses, of whatever type, is currently being monitored with periodic follow-up and with imaging systems, at specialised health structures, in so far as, in tissue valve prostheses there may occur alterations of the valve leaflets owing to calcification phenomena, which may lead to an altered functionality of the said valve prostheses, whereas in mechanical valve prostheses, the state of operation of the movable closing and opening elements, typically disks or half-disks made of pyrolytic carbon, may be jeopardized by trombo-embolic phenomena, which can be mitigated and controlled with an adequate anticoagulant therapy.
Since the number of patients with implanted cardiac systems is increasing considerably, it would be useful for the community at large to have available sensorized valve prostheses, which can interact with an external monitoring terminal, having, for example, the size and weight of a smartphone or tablet, to make it possible to check at home the state of operation of the said valve prostheses, so that a patient can go to the specialised health structure when said monitoring terminal detects an anomaly in operation of the sensorized prosthesis and issues a warning.
It is evident that such a monitoring system could improve the quality of life of patients with implanted valve prostheses, also reducing mortality of patients in the case where the said monitoring system indicates situations of alarm related to a highly probable state of deterioration of the valve prosthesis, so that the patient himself can be alerted and can go to a specialised health structure for possible early replacement of the said heart valve prosthesis before the latter is damaged.
As prior art, reference may be made to the examples cited below.
The U.S. Pat. No. 5,487,760 refers to a heart valve prosthesis of a mechanical type, equipped with a sensor of a capacitive or inductive type or a vibration sensor, for example of the piezoelectric type, connected to an electronic microcircuit set between the external structure of the valve and the material that coats the suture ring, in order to detect signals correlated to the opening and closing movement of the leaflets of the said heart valve prosthesis and also describes how to energize said internal microcircuit and how to interact therewith, through a telemetry device external to the patient. The disclosure of the patent application WO2010/062223 refers to a lead for cardiac pacing, to be inserted in the right-hand cardiac cavities or in the coronary sinus, equipped with electrodes and connected to means for measuring electrical impedance and for monitoring, through this, operation of the natural heart valves. The U.S. Pat. No. 7,643,879 describes how to sensorize a heart valve prosthesis through a physiological sensor configured for detecting the electrical signal of the heart in the proximity of a heart valve and a sensor configured for detecting haemodynamic parameters, wherein said sensor comprises a flowrate sensor for detecting the flow of the blood, or else a pressure sensor, or else a sensor for detecting deflection of the leaflets of the valve, for example of an electromagnetic, or else piezoresistive, or else piezoelectric, type or else a Hall-effect sensor, acoustic sensors, or optical sensors. Also the disclosure of the patent US2012/0296382A1 describes in a generic way a heart valve prosthesis which includes a physiological sensor and an electronic microcircuit that enables transmission of the vital physiological information detected by said sensor to means external to the patient. The U.S. Pat. No. 7,089,051 describes in a very generic way how to monitor opening of the aortic valve with a measurement of electrical impedance made between extra-valve electrodes, located in the cardiac sinus and in the great cardiac vein. The U.S. Pat. No. 5,792,194 describes a device for measuring an electrical impedance between electrodes set in the atrium and in the ventricle for measuring a useful parameter during physical activity to control cardiac stimulation (RR function) by an electrical cardiac pacing device. Also the U.S. Pat. No. 4,730,619 describes a device for regulating the electrostimulation frequency of an implanted device such as a pacemaker as a function of the variations of electrical impedance-detected in this case between electrodes set on an electrocatheter inserted within the cardiac cavity and an electrode located on the case of the said pacemaker. Finally, the U.S. Pat. No. 5,902,325 describes a cardiac-stimulation apparatus that detects the cardiac capture by means of a measurement of electrical impedance.
From the known art it may be evinced that the measurements of electrical impedance or rheographic measurements made between two or more electrodes inserted in cardiac pacing lead is a technique that has been used for more than thirty years, is by now consolidated, is easy to implement, and presents high technological reliability. So far the rheographic technique has been used basically for detecting mainly parameters (minute ventilation or atrio-ventricular impedance) for adapting pacing rate in implantable electrical cardiac pacing device (rate responsive pacing) and, when it has been used for detecting the opening movement of a natural valve, as in U.S. Pat. No. 7,089,051 considered above, it has been carried out between electrodes set in pacing leads inserted in the coronary sinus and great cardiac vein, hence obtaining, given the extravalvular position of the electrodes, a measurement of electrical impedance that is correlated to the movement of the valve leaflets but that may be markedly falsified by the variations of the volumes of blood present in the cardiac cavities and in the vessels themselves in which the measurement electrodes are inserted and by the considerable changes in shape of the cardiac muscle.